Numeric poly var support

[bobzhang]

Note we are planning to provide numeric poly var support so that

#"1" is going to be compiled as 1 instead of "1"

Ideally, we should allow user to write #1 directly since it is compiled to 1 instead of "1"
Some more context are provided here: rescript-lang/rescript-compiler#5026

For the formal rules it would be:

# 0
# [1-9][0-9]*

Also an extra overflow check is needed

[gaku-sei]

Sorry @bobzhang if #1 is accepted in the future and compiles to 1 can we keep #"1" to compile to "1" (even though I understand it's an escape hatch it's a neat one ^^)?
There are several reasons for that, but the main one is backward compatibility (actually we do use #"number" here and there already 😁).

I wonder, why will numeric variants be compiled to numbers ?

[bobzhang]

@gaku-sei it is to provide good interop with JS API which expects enums or return enums. There is currently no easy way to do this without a conversion; and it is a pain point for production users.
What's your use case for making #"1" to "1"?

[IwanKaramazow]

@bobzhang is there a reason we restrict this to non-float numbers? (I'll document this for posteriority)

[bobzhang]

@IwanKaramazow the main use case is for passing and receiving enums.

This is is the quote from some users:

i think positive integers covers 99% of our use cases

Float can be a bit tricky, since 0.33 may not be representable in IEEE 754.
FYI: https://github.com/rescript-lang/rescript-compiler/blob/master/jscomp/ext/ext_string.ml#L510 this is what we used to determine if it is the hash number.

Things could be done in the front-end:

• support #1
• gives an error for #"1" since this can be confusing
• detect int overflow

In the future, we could support things like #0x01 (the hex format) which should be in no conflict with what we have right now. Note this addition is also a good example to demonstrate the value of rescript syntax.

[IwanKaramazow]

Thanks for the background, will implement.

[gaku-sei]

There is currently no easy way to do this without a conversion; and it is a pain point for production users.

Makes actually, absolutely makes sense.

What's your use case for making #"1" to "1"?

We use to interface with tailwind and concat the poly variant with some other string. In that case the new syntax happens to work, but I was concerned that some cases wouldn't work (hence the idea to differentiate #"1" and #1 as it seems they cover 2 different use cases 😕

[bobzhang]

@gaku-sei I think this still works since you mentioned concatenation.

1+"px" === "1" + "px"

[chenglou]

Yeah kinda agree that maybe #"1" should be supported. Otherwise a bit inconsistent

[bobzhang]

We could support #"1" syntactically, but it will be encoded as 1, so it may bring confusion instead of consistency.
Note for structural types, the encoding has to be simple and consistent.

[chenglou]

Oh, if #"1" is encoded as 1 then nevermind. Would rather have a good error message or formatted format to #1. But I was saying that it was confusing to not support #"1" as "1"

[cannorin]

i think positive integers covers 99% of our use cases

I'm trying to create a tool to generate ReScript bindings from TypeScript type definitions (.d.ts), and I've been encountering so many negative integers, even in popular packages:

• typescript: https://github.com/microsoft/TypeScript/blob/9d443b76aac0832d7f3c890441264d39307fe31a/lib/typescript.d.ts#L1714
• node: https://github.com/DefinitelyTyped/DefinitelyTyped/blob/ee4131447a3b01d3a0463e2d2794df0302b6e711/types/node/v14/tty.d.ts#L16
• semver: https://github.com/DefinitelyTyped/DefinitelyTyped/blob/f7ec78508c6797e42f87a4390735bc2c650a1bfd/types/semver/classes/semver.d.ts#L27

It seems people often use 1 | -1 to indicate left/right or positive/negative, 1 | 0 | -1 to represent larger/equal/smaller, and -1, -2, ... for special/erroneous cases, which should be better represented as type rather than making it just int.

Also, it kind of contradicts with the fact @deriving(jsConverter) for non-poly variant supports negative values.

@deriving(jsConverter) can be used as a workaround, but it introduces an unnecessary variant type each time something like 1 | 0 | -1 is used.

[stale]

The rescript-lang/syntax repo is obsolete and will be archived soon. If this issue is still relevant, please reopen in the compiler repo (https://github.com/rescript-lang/rescript-compiler) or comment here to ask for it to be moved. Thank you for your contributions.